The aim of
the study is to assess whether attending to nursery is associated with high
frequency of respiratory infections.
It is useful to compare proportions of infection by category of assistance
to the nursery, we do this by comparing percentages of rows and calculating
the Chi square test for association between these two variables.
In this example, the variable result is respiratory infection (dependent
variable) and assistance to the nursery as the exposure variable
(independent variable), which explains the frequency of infection.
To measure the association between exposure and outcome in a 2 x 2 table we
can calculate the risk ratio (RR) or odds ratios (OR).